Disk drives are information storage devices that use a rotatable disk with concentric data tracks containing the information, a head or transducer for reading and writing data with respect to the data tracks, and an actuator connected to a carrier for the head for moving the head to the desired track and maintaining it over the track centerline during read or write operations. There are typically a plurality of disks separated by spacer rings. The disks are stacked on a hub that is rotated by a spindle motor. A housing supports the spindle motor and head actuator and also surrounds the head and disk(s) to provide a substantially environmentally sealed container for the head-disk interface.
In conventional magnetic recording disk drives, the head carrier is an air-bearing slider that rides on a cushion of air above the disk surface when the disk is rotating at its suspension that connects the slider to the actuator. The slider is either biased toward the disk surface by a small spring force from the suspension, or is self-loaded to the disk surface by means of a negative-pressure air-bearing surface on the slider.
To improve the wear resistance of the disk and to maintain consistent magnetic properties, it is desirable to make the disk surface as smooth as possible. However, a very smooth disk surface may create a problem typically known the art as stiction. Stiction may occur after the slider has been in stationary contact with the disk for a period of time, resulting in the slider resisting translational movement or sticking to the disk surface. Stiction is caused by a variety of factors, including static friction and adhesion forces between the disk and slider created by the lubricant on the disk. Stiction in a disk drive can result in damage to the head and/or disk when the slider suddenly breaks free from the disk surface when disk rotation is initiated. In addition, damage to the suspension between the actuator and the slider may occur after the disk suddenly rotates. In some disk drives, such as low-power disk drives used in laptop and notebook computers, the spindle motor may simply be unable to initiate rotation or achieve operating speed because of the adhesion forces that cause excessive drag between the slider and the disk.
Disk drives without load/unload ramps operate with the slider in contact with the disk surface during start and stop operations when there is insufficient disk rotational speed to maintain the air bearing that lifts slider above the surface of the disk. To minimize the effect of stiction, disk drives without load/unload ramps often use a dedicated landing zone where the slider is parked when the drive is not operating. Typically, the landing zone is a specially textured non-data region of the disk. In contrast to disk drives without load/unload ramps, load/unload disk drives address the stiction problem by mechanically unloading the slider from the disk when the power is turned off, and then loading the slider back to the disk when the disk has reached a speed sufficient to generate the air bearing. The loading and unloading is typically done by means of a ramp that contacts the suspension when the actuator is moved away from the data region of the disk. The slider is thus parked off the disk surface with the suspension supported in a recess of the ramp.
Inherent failure mechanisms exist in disk drives either with or without load/unload ramps that can result in the slider coming to rest on the disk. For example, external shocks can displace the slider from the landing zone or the load/unload ramp, and errors in the microcode controlling the actuator can inadvertently cause the slider to land on the disk.
Stiction problems are not limited to conventional air-bearing disk drives. Liquid-bearing disk drives exhibit similar problems. Thus, in both air-bearing and liquid-bearing disk drives, it is desirable to find a means for not placing into a power saving sleep mode those disk drives that are experiencing stiction. Operation of a stiction-prone hard disk drive in a power saving sleep mode, followed by periods of spinup will exacerbate the stiction problem as it potentially allows the offending slider to repeatedly restick itself to the disk surface.